Boiler

ABSTRACT

A boiler is provided with a radiation heat transfer section in its combustion chamber, which has therein, at least one regenerative-heating burner system including a pair of burners each with a regenerative bed. The burners receive combustion air and exhaust combustion gas which passes through the regenerative beds. Combustion is alternately effected in one of the burners and combustion gas is passed into the other burner, and exhausted through the corresponding regenerative bed of this other burner. Surplus thermal energy which is not completely consumed in the radiation heat transfer section is recovered in the regenerative bed. Combustion air than passes through the heated regenerative bed to heat the air. The boiler temperature is kept flat across the boiler. That is, the temperature is kept almost constant across the combustion chamber. This is done by maintaining a high rate of forced supply of more than 60 m/s for the combustion air. Also, the combustion air is heated to above the ignition point of the fuel, that is, about 800° C. These two factors increases thermal efficiency while reducing NO x  emissions.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/544,562, filedOct. 18, 1995, and now U.S. Pat. No. 5,626,104 which is acontinuation-in-part application of Ser. No. 08/199,205 filed Feb. 28,1994, and now U.S. Pat. No. 5,522,348.

FIELD OF THE INVENTION

The present invention relates to a boiler, and in particular to animprovement of a combustion chamber in the boiler.

BACKGROUND ART

In general, most conventional boilers employ aone-directional-combustion-type heat transfer mechanism. An example ofthat boiler is, as shown in FIG. 23A, constructed such that a burner 104is installed at one end of a combustion chamber, from which burner, acombustion gas is blown, and during discharge of the gas from anotherend of the same combustion chamber, a heat of the gas is transferred towater in the boiler tube by means of a radiation heat transfer and aconvection heat transfer, to thereby generate steam. The combustionchamber is divided into a radiation heat transfer section 101 forproviding radiation heat to the boiler water, and a convection heattransfer section 102 for providing convection heat to the boiler water.In the radiation heat transfer section 101, although both flametemperature and heat absorption of the boiler are high (see FIG. 23B),the heat from the combustion gas is not completely transferred to theboiler water, which thus requires installing the convection heattransfer section 102 at the downstream site in order to recover thecombustion gas heat. In the absence of such convection heat transfersection 102, the temperature of the exhaust gas will increase, giving abad influence on the environment and also lowering thermal efficiency.

There has been known a boiler of the type which superheats a saturatedsteam in a superheater section provided therein. For example, as shownin FIG. 24A, in this sort of boiler, a superheater section 103 isdefined between a radiation heat transfer section 101 and a convectionheat transfer section 102. With this arrangement, a saturated steamgenerated in both radiant and convection heat transfer sections 101, 102is superheated in the superheater section 103 so as to obtain asuperheated steam. Alternatively, as in FIG. 25A, some of boilers ofthis sort have the superheater section 103 defined behind the radiantand convection heat transfer sections 101, 102 so that a saturated steamgenerated therein is superheated at the extreme downstream end of thecombustion gas path. In those boilers, a typical way to adjust atemperature required for the superheating is by providing a bypass whichdoes not pass through a heat exchanger in the superheater section 103,thereby controlling the amount of combustion gas flowing through thesuperheater section 103, or by cooling the superheated steam by way of aheat exchange with the boiler water and the like or by means of acooling water being sprayed in the superheated steam.

However, the convection heat transfer section 102 is undesirably low interms of a heat absorption of the boiler, resulting in the need forincrease of the heat transfer area of that particular section in anattempt to recover heat sufficiently and raising the problem that thefurnace thereof also requires larger dimensions. Further, theconventional furnace employed in the boiler has been found defective inthat the heat absorption of the boiler in the radiation heat transfersection 101 is changeable extraordinarily, which does not provide auniform heating of a boiler water flowing in the water tubes or whichmay become full of steam. To prevent this problem, it is necessary toinsure the circulation of the boiler water, and therefore, anotherproblem is posed: The dispositions of heat transfer tubings are limited,and a pump and power are required for executing a forced circulation ofthe boiler water that need more initial and running cost.

In this conventional boiler with superheater, furthermore, there hasbeen such problem that its damper or duct is damaged by a hightemperature of combustion gas flowing in the bypass, an that, in thecase of lowering a temperature by spraying water in the superheatedsteam, a thermal efficiency will become poor. Still further, to disposethe superheater section 103 behind the convection heat transfer section102 will also make poor the thermal efficiency, though it may obtain alow-temperature superheated steam. In addition thereto, there will bethe problem that if the temperature of superheated steam is lower than apredetermined temperature, a proper improvement will be needed forincreasing the heat transfer area of the superheater.

DISCLOSURE OF THE INVENTION

It is a first purpose of the present invention to provide a boiler whichpermits increasing the heat absorption of the boiler and making uniformthe distribution of heat absorption of the boiler in the whole furnace.The second purpose of the invention is to provide a boiler which makesit easy to control the temperature of superheated steam without changingthe structure and thermal valance. Also, the third purpose of theinvention is to provide a boiler which allows for increasing the amountof heat to be recovered, while keeping constant the heat transfer areain the boiler. Further, the fourth purpose of the invention is toprovide a boiler which allows control of temperature zones.

In order to achieve those purposes, in accordance with the presentinvention, there is provided a boiler which has a radiation heattransfer section in which at least more than oneregenerative-heating-type burner system is disposed, theregenerative-heating-type system being provided with a regenerative bedand being arranged such that, through the regenerative bed, a combustionair is supplied into the burner and a combustion gas exhausted from thefurnace of boiler, while causing a flow of the combustion air and a flowof the combustion gas to be changed over relative to each other, andthen allowing the combustion air to be supplied through the regenerativebed which is heated by a heat of the combustion gas.

In one aspect, as may be required, the boiler in accordance with thepresent invention may have a convection heat transfer section providedwith an exhaust means for introducing a part of the combustion gas fromthe radiation heat transfer section and directly exhausting that part ofcombustion gas to the outside of a combustion chamber without passingthe same through the regenerative bed.

In another aspect, the boiler in accordance with the invention may be soconstructed that a plurality of the above-mentionedregenerative-heating-type burner systems are disposed in the directionalong the flow of a boiler water, that two regenerative-heating-typeburners forming a pair from those plural burner systems are disposed ina direction transversely of the flow of boiler water, and that acombustion is controlled per one of the burner systems in such a manneras to define a plurality of temperature zones in the direction along theflow of boiler water, thereby allowing for control of a distribution ofheat absorption rate in the whole furnace.

In still another aspect, the boiler in accordance with the invention mayhave a radiation heat transfer section in which at least more than oneregenerative-heating-type burner system is disposed, theregenerative-heating-type system being provided with a regenerative bedand being arranged such that, through the regenerative bed, a combustionair is supplied into the burner and a combustion gas is exhausted fromthe furnace of the boiler, while causing a flow of the combustion airand a flow of the combustion gas to be changed over relative to eachother, and then allowing the combustion air to be supplied through theregenerative bed which is heated by heat of the combustion gas, whereinthe boiler further has a superheater section for extracting a part ofthe combustion gas from the radiation heat transfer section, thensuperheating a saturated steam and directly exhausting the combustiongas to the outside of a combustion chamber without passing the samethrough the burners. In this particular mode, it is preferable that theamount of combustion gas to be introduced into the superheater sectionshould be controlled in response to the temperature of the superheatedsteam.

Accordingly, by means of the boiler in this invention, the boiler wateris heated only by the radiation heat originated from the combustion gas,which maintains the furnace heat absorption of the boiler in a highstate and makes its distribution uniform. Further, the combustion gas isexhausted, keeping its high temperature, through an inoperative one ofthe burners, to the outside of the combustion chamber, and thus, theheat of the combustion gas is recovered in the correspondingregenerative bed and the gas itself is exhausted, with a relatively lowtemperature, to the atmosphere. Then, the thus-recovered heat is used topreheat a combustion air and returned into the combustion chamber, henceimproving the thermal valance in the boiler. For this reason, there isno need for providing a convention heat transfer section and a smallheat transfer area of the boiler furnace suffices in comparison with theconventional boiler. For example, as compared with the conventionalboiler, it is possible to reduce the heat transfer area by approx.30%-60% in order to obtain the same amount of steam. In addition, theboiler is capable of raising the thermal efficiency up to approx. 95%,which means to improve the thermal efficiency higher by 5%-10% than thatof the conventional boiler. Moreover, the boiler in accordance with theinvention does not require provision of the convection heat transfersection, thus simplifying its structure and reducing the group of watertubes, which contributes not merely to decreasing the area where theboiler is installed, but also to low costs. Even in the event that theconvection heat transfer section needs to be provided in the boiler, itwill be required only to extract a part of the combustion gas for supplyto that section, and therefore, to reduce the heat transfer area willnot result in lowering the heat absorption of the boiler, but will lowerthe temperature of exhausted gas, leading thus to a high heatingefficiency economically.

Furthermore, in accordance with the boiler of the present invention, ifthe plural regenerative-heating-type burner systems are disposed in adirection orthogonal to a direction wherein the boiler water flows, insuch a manner as to define plural temperature zones in a direction alongthe flowing direction of boiler water, then the combustion may becontrolled in each of the burner systems to define different zones ofdifferent combustion gas temperatures in the radiation heat transfersection, thereby permitting controlling of the distribution of heatabsorption rate in the whole furnace, as desired.

Yet further, in accordance with the boiler of the present invention,since part of the combustion gas is extracted and supplied to thesuperheater section to superheat a superheated steam, it is possible tocontrol the amount of extracted combustion gas and therefore, incontrast to the conventional boiler with superheater having the sameheat transfer area, the temperature of the superheated steam can easilybe controlled by such control of the amount of extracted combustion gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an generation principle diagram of a boiler in accordancewith the present invention, and FIG. 1B is a graph showing the heatabsorption of the boiler. FIG. 2A is an operation principle diagram ofone embodiment of the boiler in accordance with the invention, and FIG.2B is a graph showing the heat absorption of the boiler. FIG. 3A is across-sectional view of a once-through-type water tube boiler to whichis applied the present invention, and FIG. 3B is a longitudinallysectional view of the same boiler. FIG. 4A is a cross-sectional view ofanother embodiment of the once-through-type water tube boiler to whichthe present invention is applied, and FIG. 4B is a longitudinallysectional view of the same boiler. FIG. 5A is a longitudinally sectionalview of a natural-circulation-type water tube boiler, in which thepresent invention is applied along the water tubes, and FIG. 5B is alongitudinally sectional view showing the same boiler along the wallsthereof. FIG. 6A is a longitudinally sectional view showing anotherembodiment of the natural-circulation-type water tube boiler, in whichthe present invention is applied along the water tubes, and FIG. 6B is alongitudinally sectional view showing the same boiler along the wallsthereof, and FIG. 6C is a cross-sectional view of the same boiler. FIG.7A is a longitudinally sectional view showing a vacuum boiler in thedirection intersecting the water tubes of the boiler, to which thepresent invention is applied, FIG. 7B is a longitudinally sectional viewshowing the same boiler along the water tubes thereof, and FIG. 7C is across-sectional view of the same boiler. FIG. 8 is a longitudinallysectional view showing another embodiment of the vacuum boiler to whichis applied the invention. FIG. 9A is a cross-sectional view of a flueboiler to which the invention is applied, and FIG. 9B is alongitudinally sectional view of the flue boiler. FIG. 10A is across-sectional view showing another embodiment of the flue boiler towhich is applied the invention, and FIG. 10B is a longitudinallysectional view of the same boiler. FIG. 11A is an operation principlediagram of another mode of boiler in accordance with the invention, andFIG. 11B is a graph showing heat absorption of the boiler in the sameboiler. FIG. 12A is an operation principle diagram of a boiler withsuperheater in accordance with the invention, and FIG. 12B is a graphshowing heat absorption of the boiler in the same boiler. FIG. 13A is anoperation principle diagram of a boiler with superheater in accordancewith the invention, and FIG. 13B is a graph showing heat absorption ofthe boiler in the same boiler. FIG. 14 is an operation principle diagramshowing one way for adjusting the temperature of superheated steam inthe boiler with superheater in accordance with the present invention.FIG. 15 is an operation principle diagram showing another example ofadjusting the temperature of superheated steam in the boiler withsuperheater in accordance with the invention. FIG. 16A is alongitudinally sectional view showing a natural-circulation-type watertube boiler along the water tubes thereof, to which is applied theboiler with superheater of the present invention, and FIG. 16B is alongitudinally sectional view showing the same boiler along the wallsthereof, and FIG. 16C is a cross-sectional view of the same boiler. FIG.17A is a longitudinally sectional view showing an over-fired- and-once-through-type water tube boiler to which is applied the boiler withsuperheater of the present invention, and FIG. 17B is a longitudinallysectional view showing an underfired- and -once-through-type water tubeboiler. FIG. 18 is a perspective view of the once-through-type watertube boiler to which the present invention is applied. FIG. 19 is alongitudinally sectional view of the boiler shown in FIG. 18. FIG. 20 isa cross-sectional view of the boiler shown in FIG. 19. FIG. 21 is aschematic diagram which explanatorily shows one example ofregenerative-heating-type burner systems used in the boiler of thepresent invention. FIG. 22 is a schematic diagram which explanatorilyshows another example of regenerative-heating-type burner systems. FIG.23A is an operation principle diagram showing a conventional boiler, andFIG. 23B is a graph showing heat absorption of the boiler in the sameboiler. FIG. 24A is an operation principle diagram showing aconventional boiler with superheater, and FIG. 24B is a graph showingheat absorption of the boiler in the boiler. FIG. 25A is an operationprinciple diagram showing another conventional boiler with superheater,and FIG. 25B is a graph showing heat absorption of the boiler in thesame boiler. FIG. 26 is a graphic representation of the operatingconditions of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a specific description will be made of the construction ofthe present invention, with reference to the embodiments shown in thedrawings.

FIG. 1A shows one example of an operation principle diagram for a boilerin accordance with the present invention. This boiler has a combustionchamber which is formed only by a radiation heat transfer section 15,where at least one unit of regenerative-heating-type burner system 1 isprovided in a surface of wall of furnace. In the case of the presentembodiment, the regenerative-heating-type burner system 1 comprises, incombination, at least one pair of burners 2, 3 and one pair ofregenerative beds 5, the burners being disposed on the same wall offurnace, whereby a combustion may be alternately effected by one ofthose two burners 2, 3, while allowing a combustion gas generated to beexhausted through another of the same burners 2, 3 and regenerative beds5.

In this connection, the regenerative-heating-type burner system 1 is notlimitative in structure and combustion method, but as shown in FIG. 21for instance, the system may be constructed such that the wind boxesrespectively of the foregoing pair of burners 2, 3 may be selectivelyconnected, by means of four-way valves 11, with a combustion air supplysystem 7 for supplying a combustion air and a combustion gas exhaustsystem 8 for exhausting a combustion gas, respectively, so that, thecombustion air may be supplied and the combustion gas be exhausted,through their corresponding regenerative beds 5. At this moment, thosecombustion air supply and combustion gas exhaust systems 7, 8 may beconnected selectively, by the four-way valves 11, with one of the windboxes respectively of the burners 2, 3. For example, it may be soarranged that a combustion air supplied by a forces draft fan 9 issupplied into the wind box while at the same time a combustion gasgenerated is drawn and exhausted by an induced draft fan 10 out of thewind box to the atmosphere as shown in FIG. 21 for example. Further, afuel may be selectively supplied through a three-way valve 13 into oneof the two burners 2, 3. Designation 18 denotes a heat exchanger throughwhich the boiler water flows. In the present embodiment, there areprovided nozzles 6, 6 in such a manner as to inject a fuel from aninward peripheral surface made of a refractory material which forms aburner throat and cause the fuel to intersect the flow of a combustionair passing through that burner throat. With regard to the nozzles, 6,6, only one of them may be embeded in the burner throat, which certainlysuffices for this particular purpose, but more than two nozzles may bedisposed equidistantly in a direction circumferentially of the burnerthroat, which will enable adjusting a fuel blockage ratio, i.e. a ratioat which the injected fuel blocks or occupies the cross-sectional areaof the burner throat so as to permit for varying the characteristics formixing the fuel with air, in which case also, a flame may be created atthe center of the burner throat. In this particular mode, it is possibleto vary an angle between the flow of fuel jetted from the nozzles 6, 6and the flow of air so as to change a speed for mixing the fuel and air,and in that way, the length of flame created thereby may be varied. Thefuel is not limited to a liquid fuel or gaseous fuel, but may be apulverized coal fuel or the like. Also, the disposition and structure ofthe fuel nozzles are not specifically limitative. In accordance with thepresent invention, it may be so arranged that the fuel is supplied intwo steps, as for example, the fuel may be supplied to a upstream sidewithin the wind box and then supplied to a point adjacent the exit ofthe burner throat, whereby a part of the fuel may be burnt by a wholeamount of combustion air to perform a first combustion and thereafteranother unburnt part of the fuel be burnt by a residual oxygen remainingin a combustion gas generated, to thereby perform a second combustion.Further, the regenerative bed 5 is not specifically limitative, and maybe formed into a cylindrical body with a honeycomb-like structure whichis made of a fine ceramics.

As constructed above, a pair of regenerative-heating-type burners 2, 3are each alternately brought in operation for the combustion, so that acombustion gas generated thereby is exhausted through the combustion gasexhaust system 8 associated with one of those two burners which is beinginoperative for the combustion, and then a heat of the combustionexhausted is recovered by the corresponding regenerative bed 5. Afterlapse of a given period of time, the inoperative burner 3 (or 2)opposite to the operative one is then brought in operation forcombustion, while exhausting a combustion gas generated thereby throughthat opposite burner 2 (or 3) which has been operative for combustion.At this moment, the combustion air absorbs a heat stored in theregenerative bed 5 associated with the burner 3 (or 2) which hadpreviously been inoperative and is thereby preheated at a hightemperature, for example, at 700° C.-1,000° C. before being suppliedinto the burner. Operation for alternating those combustion and exhaustmay be effected at the interval of 20 sec.-2 min. for instance, butpreferably at the interval of 20 sec.-40 sec. or each time that thetemperature of combustion gas being exhausted reaches a controlledtemperature say, at approx. 200° C.

The heat absorption of the boiler in the present embodiment is indicatedin FIG. 1B.

The boiler shown in FIG. 1A is embodied more specifically in FIG. 3A,FIGS. 3B, 4A and 4B. These embodiments are applied to aonce-through-type water tube boiler. This boiler is provided with agroup of water tubes 21, 21, . . . , 21 embedded in the surface of wallof a cylindrical furnace 20, and so constructed that a boiler water issubject to heating during its being supplied upwardly through the watertubes 21, . . . , 21 from the downward side, then only a steam isextracted in the steam separator 22 disposed at the upper end side, anda hot water gained is again supplied together with a boiler water fromthe downward side into the boiler. Mounted upon the top portion 23 ofthe foregoing furnace 20 are a pair of regenerative-heating-type burners2, 3, by means of which, a flame is created in parallel with the watertubes 21 and thereafter a gas is exhausted from the upper inoperativeburner. Alternately, as shown in FIGS. 4A and 4B, the burners 2, 3 maybe disposed side by side in the bottom portion 24 of the furnace 20,whereby a flame is created towards the furnace top portion 23 and acombustion gas generated is exhausted from the side of that bottomportion 24.

FIG. 2A shows another embodiment. According to this embodiment, at leasttwo units of the regenerative-heating-type burner systems 1 are disposedat two opposed walls of the furnace, respectively, with such anarrangement that a combustion gas is blown out and exhausted between thetwo opposed burners 2, 3, without flowing the combustion gas between thecommon adjoining two burners 2, 3 disposed on the same wall of furnace.For example, as viewed from the figure, a combustion gas to be blownfrom the upper burner 2 provided in the left-side furnace wall will besubject to heat absorption in the upper burner 3 provided in theright-side furnace wall, recovering thus a heat from the combustion gas,and then discharged therefrom to the atmosphere. On the other hand, acombustion gas to be blown from the lower burner 2 provided in theright-side furnace wall will be subject to heat absorption in the lowerburner 3 provided, in the left-side furnace wall, recovering a heat fromthe gas, and then discharged therefrom to the atmosphere. Subsequentthereto, though not shown, with the combustion alternated between theburners, a combustion gas will be blown from the lower burner 3 on theleft side, while also a combustion gas will be blown from the upperburner 3 on the right side. Then, each of the gases will be exhaustedfrom the respective burners facing oppositely towards those operativeburners. In this case, the heat absorption of the boiler is obtained asshown in FIG. 2B.

FIGS. 5-10 illustrate the specific embodiments of the foregoing boilershown in FIG. 2A. FIGS. 5 and 6 show an embodiment applied to anatural-circulation-type water tube boiler, wherein a lower drum 25 isconnected with an upper drum 26 for a flow communication therebetween bymeans of water tubes 21, 21, . . . , 21 and a downcast pipe 27, so thata boiler water flowing upwardly in those water tube groups 21, 21, . . ., 21 is again flowed downwardly through the downcast pipe 27 when thewater reaches the upper drum 26, thereby causing the water to becirculated in a natural way. The natural circulation of boiler water iseffected due to a difference in density between the mixture of steam andhot water in the water tubes 21 heated extremely by the radiation heatand the water in the downcast pipe 27 which is not heated at all orgently heated by virtue of the water tubes 21 shielding the pipe. In thepresent embodiments, it may be so arranged that four units of burnersystems (see FIGS. 5A and 5B) or two units of burner system (see FIGS.6A, 6B and 6C) are disposed such as to form flames in a directiontransversely of the water tube groups 21, 21, . . . , 21, i.e. in theright and left directions as viewed from the figures. The illustratednatural-circulation-type water tube boilers each have two burners 2, 3which form a regenerative-heating-type burner system 1 and are providedin the right-side and left-side furnace walls. According thereto, acombustion gas to be blown from the burner 2 or 3 at one of the furnacewalls will pass across the interior of furnace into the correspondingburner 3 or 2, and be exhausted therefrom, so that a heat of thecombustion gas may be recovered by the corresponding regenerative bed 5,and thereafter, the gas will become a low-temperature exhaust gas and beexhausted out to the atmosphere. Then, with the combustion alternatedbetween the burners, a combustion air, which has been preheated throughthe foregoing regenerative bed 5 storing the heat of that combustiongas, will be supplied to the burner, allowing a high-temperaturecombustion gas to be obtained with a small amount of fuel and alsocausing the same gas to be exhausted through the burner and regenerativebed at another opposite furnace wall. At this point, as shown in FIG.5A, 5B or 6A, the downcast pipe 27 is shielded from the combustion gas,because, according to the present natural-circulation-type water tubeboiler, that downcast pipe 27 is disposed centrally thereof andinterposed or sandwiched between the walls which are formed by the watertubes 21. The boiler further has another groups of water tubes 21, 21, .. . , 21 formed at both lateral wall surfaces thereof.

FIGS. 7A, 7B, 7C and 8 illustrate embodiments of the present inventionapplied to a vacuum boiler. The vacuum boiler has a tubing 28 disposedin the upper half portion thereof, through which tubing a boiler waterflows, and has an area lower than such upper half portion, where aboiler water 30 is reserved. Disposed within the boiler water 30 is aflue 29 forming a combustion chamber, both ends of which are providedrespectively with a pair of burners 2, 3. Referring to FIGS. 7A to 7C,it is to be therefore understood that there are provided two units ofregenerative-heating-type burner systems 1, each being disposed in theright-side furnace wall on the same plane and in the left-side furnacewall on the same plane, respectively. With this structure, the mutuallyopposed burners are communicated with each other through the duct 29,hence permitting a combustion gas to be blown and exhausted among thoseopposed burners. Or, alternatively, as shown in FIG. 8, a pair ofburners 2, 3 may each be disposed in both mutually opposed walls offurnace and the two burners 2, 3 be communicated with each other throughone duct 29.

FIGS. 9A and 9B as well as FIGS. 10A and 10B show embodiments of thepresent invention applied to a flue boiler. The flue boiler has a lowerhalf portion in which a boiler water 30 is reserved, with a duct 31extending through the boiler water 30, and further has a spacing 32defined in the upper portion thereof, through which spacing, a steam isto be removed. A combustion chamber is formed by the duct 31, havingboth ends with which are provided burners 2, 3 forming aregenerative-heating-type burner system, hence permitting a combustiongas to flow in the duct 31. Of course, as in FIGS. 10A and 10B, theregenerative-heating-type burner system 1, and the duct 31 which acts asa combustion chamber are not limited to one unit or one piece, but maybe provided in a plural form.

FIG. 11A shows still another embodiment of the present invention. Inthis embodiment, a radiation heat transfer section 15 is constructedtogether with at least one unit of regenerative-heating-type burnersystem, and additionally, a convection heat transfer section 16 isdefined in combination therewith. It is so arranged that a part ofcombustion gas may be extracted, as required, from the convection heattransfer section 15. The heat absorption of the boiler is obtained asshown in FIG. 11B.

FIGS. 12A and 13A show operation principle diagrams concerning a boilerwith superheater to which the present invention is applied. The boilershown in FIG. 12A has a radiation heat transfer section 15 and asuperheater section 17 defined therein, with more than one unit ofregenerative-heating-type burner system 1 being provided at theradiation heat transfer section 15, the arrangement of the boiler beingsuch that a part of a combustion gas flowing in the burner system 1 willbe extracted and flowed to the superheater section 17, to therebysuperheat a saturated steam generated in the radiation heat transfersection 15. Otherwise stated, the exhaust system 8 of theregenerative-heating-type burner system 1 is connected with the exhaustsystem 14 of the superheater section 17, so as to cause a part ofcombustion gas to be exhausted through the superheater section 17 andflowed through the regenerative bed 5 of an inoperative burner for finalexhaust. In this case, the heat absorption of the boiler is obtained asshown in FIG. 12B. Alternately, as shown in FIG. 13A, more than one unitof regenerative-heating-type burner system 1 may be provided in both twoopposed walls of the radiation heat transfer section 15, to therebypermit a combustion gas to be blown and exhausted among the mutuallyopposed burners disposed at the different walls, so that a part of thecombustion gas may be extracted to the superheater section 17 which isformed between those two opposed walls, each of which is provided withthe burner system 1, and such part of combustion gas be exhaustedtherefrom. In that case, the heat absorption of the boiler is obtainedas shown in FIG. 13B.

FIGS. 14 and 15 show one example of way for adjusting the temperature ofsuperheated steam in the foregoing boiler with superheater shown inFIGS. 12A and 13A. Designation 36 denotes a temperature sensor,designation 37 denotes a damper operable for adjustment of exhaust fromthe superheater section 17, designation 38 denotes an actuator which iscontrolled responsive to the temperature sensor 36, and designation 39denotes a link mechanism for transmitting a motion of the actuator 38 tothe damper 37. With such structure, in the case where a temperature ofsuperheated steam detected by the temperature sensor 36 exceeds over apredetermined value, the actuator 38 will be operated to close thedamper 37, preventing leakage of a part combustion gas into thesuperheater section 17, and conversely, if the superheated steamtemperature is below that predetermined value, the actuator 38 will beoperated to open the damper 37, allowing a part of combustion gas to beexhausted through the superheater section 17. In this regard, an amountof combustion gas flowing through the superheater section 17 may beadjusted by controlling the degree for opening or closing the damper 37.

FIGS. 16A, 16B and 16C as well as FIGS. 17A and 17B illustrate specificembodiments of the above-described boiler with superheater shown inFIGS. 12A through 15. FIG. 16A to 16C show an embodiment ofnatural-circulation-type water tube boiler. This boiler is of thestructure wherein exhaust holes 33 are formed at a center of the furnacewall of the boiler such that each of them is defined between adjoiningtwo of plural water tubes 21, and wherein those exhaust holes 33 are ina flow communication with the superheater section 17 through flues 34,thereby permitting a saturated steam to be superheated by a part ofcombustion gas. In this regard, the saturated steam is extracted from anupper drum 26 and then flowed through a heat exchanger 35 provided inthe superheater section 17. There is a temperature sensor 36 disposed atthe exit of the heat exchanger 35, with such an arrangement that theamount of combination gas to be introduced into the superheater section17 may be controlled properly in accordance as the sensor 36 senses thetemperature of superheated steam at the exit of the heat exchanger. Forinstance, the damper 37 may be provided in a flue/exhaust system 40associated with the superheater, and the actuator 38 for causing openingor closing the damper 37 may be controlled its drive by means of thetemperature sensor 36. It is noted that the motion of the actuator 38 istransmitted as a rotational motion through the link mechanism 39 to thedamper 37.

FIG. 17 shows an embodiment of once-through-type boiler. This sort ofboiler, as applied to the present invention, should be so constructedthat at least more than one unit of regenerative-heating-type burnersystem is disposed at the upper portion of furnace, whereas an exhausthole 33 is provided at the bottom side of the same furnace, throughwhich exhaust hole 33, a part of combustion gas is to be extracted. Thearrangement of this particular boiler is such that a flow communicationis established between the exhaust hole 33 and the superheater section17 to permit a part of combustion gas to be exhausted through the burner3 or 2, with that part of combustion gas flowing through the superheatersection 17 before being exhausted. In the superheater section 17, thetemperature sensor 8 is provided, which detects the temperature ofsuperheated steam, and, with the detection of sensor 36, the actuator38, which operates to adjust the opening degree of the damper 37disposed at the exit of the superheater section 17, may be controlledproperly. FIG. 17B shows another embodiment of the once-through-typeboiler, according to which, the position where the burners 2, 3 aredisposed and the location of the exhaust hole 33 are set in a mannerreversal to those shown in FIG. 17A.

FIGS. 18 through 20 illustrate still another embodiment of the presentinvention. This embodiment relates to a natural-circulation-type watertube boiler capable of controlling the distribution of heat absorptionof the boiler, as desired, in the radiation heat transfer section 15.According thereto, a plurality of regenerative-heating-type burnersystems 1, . . . , 1 are disposed in a direction wherein a water issupplied upwardly, i.e. in an axial direction of the water tubes 21, soas to form a plurality of temperature zones. In the illustratedembodiment, three temperature zones are formed. In each of thetemperature zones, a pair of regenerative-heating-type burners 2, 3 aredisposed abreast with another ones in a direction orthogonal to thewater tubes, i.e. in a direction transversely of the water tubes 21, . .. , 21, whereupon two adjoining burners constitute one unit of theregenerative-heating-type burner system 1. In the present embodimentshown, on the wall of the boiler, four units ofregenerative-heating-type burner systems 1 are disposed abreast with oneanother in a direction transversely of the water tubes 21, and further,those four units of burner systems 1 are provided in three zones in theaxial direction of the water tubes (i.e. in the vertical direction),thus defining three temperature zones in that axial direction of watertubes or in the vertical direction. With such arrangement, a combustiongas blown from one burner 2 or 3 will be inhaled into another adjoiningand mating burner 3 or 2 and exhausted therefrom, which creates a flamein a horizontal direction (i.e. in the direction transversely of thewater tubes 21). Hence, combustion gases generated in each of the zonesare to be inhaled and exhausted at very and between two adjoining right-and left-side burners, thereby preventing the combustion gases fromflowing in the vertical direction and thus substantially partitioning orrestricting the flow of the gases in each of the temperature zones. Itis therefore possible to control the amount of combustion in the burnersin each of the temperature zones and set a desired temperatureindependently in each of them. This, for example, allows for settingprogressively lower combustion temperatures as the temperature zonesproceed towards the upstream nearer to the lower drum 25, while setting,by contrast, a highest combustion temperature in the temperature zone atthe most downstream adjacent to the upper drum 26, in which case, theboiler water may be heated in a high efficient way and the combustionmay be controlled to set in a high state the distribution of heatabsorption rate in the whole furnace.

Finally, it should be understood that the above-described embodimentssuggest preferred modes for carrying out the present invention, andtherefore, the invention is not limited to them, but other variousmodifications may be applied thereto without departing from the gist orscopes of the present invention. For example, theregenerative-heating-type burner system 1 described in the illustratedembodiments, which has the regenerative beds 5 fixed therein andrequires alternating the direction of combustion, or precisely stated,effecting a combustion in one of the two burners alternately, to therebychange over the flow of combustion gas and air with respect to theregenerative beds 5, is not limited to this particular construction.But, the burner system may be so constructed, as shown in FIG. 22, thatthe passages of combustion gas and air are fixed and the regenerativebed 5 is rotatable, so that the flows of combustion gas and air may bechanged relative to each other in respect of the regenerative bed 5. Inaddition, while the present embodiments utilize the four-way valve 11for connecting selectively one of the combustion air supply system 7 andexhaust system 8 with the regenerative beds 5. Yet the present inventionis not limited thereto but any other fluid passage change-over means,such as a spool-type fluid passage change-over valve.

The present invention is different from the prior art in the twofollowing ways:

(1) Combustion air is pre-heated to high temperature that is more thanthe ignition point of the fuel (800° C. or so, for example) directly bythe heat exchanger utilizing regenerator bed; and

(2) The flatness of the temperature in the combustion chamber isachieved by producing forced circulation (return circulation) ofcombustion gas in the chamber. The flow speed needed for producingforced circulation of the combustion gas is more than 60 m/s at the timeof maximum combustion, more preferable 80 m/s or 100 m/s is the mostpreferable at the time of maximum combustion.

Combustion air in burners for conventional boilers generally jets at theflow speed of 20-30 m/s or so. If the speed is faster than this, theflame is blown out. A speed for jetting air of regenerative-heating-typeburners in the prior art has not been mentioned. Air jets at the speedof 20-30 m/s is common knowledge for combustion, however. Consequently,flatness of temperature in known furnaces does not exist but partialhigh temperature areas are created, and the average temperature becomesmuch lower than the maximum limit of the temperature since the maximumtemperature in the furnace is set to be at the temperature of the hightemperature area.

This is shown in FIG. 26, at curve 201 (conventional boiler). The flator constant temperature of the invention across the boiler is shown atcurve 202.

According to the boiler of the present invention, a flow of combustionair which is jetted into the combustion chamber at a high speed of morethan 100 m/s, produces forced circulation in the combustion chamber.Further, it is not necessary to mix the fuel with the air for combustionsince the temperature of the combustion air is higher than the ignitionpoint for the fuel and the flame is stable and is not blown out becauseof this high temperature. In addition, a self recirculation ofcombustion gas and exhaust gas is made by the forced circulationproduced in the combustion chamber. Accordingly, low No_(x) due to slowcombustion, becomes possible.

Further more, the forced circulation of combustion gas is produced inthe combustion chamber by high speed jet flow of combustion air and theflatness or averaging the temperature in the combustion chamber isachieved. A partial, high temperature area is not produced (see FIG.26). This enables the average temperature in the combustion chamber tobe increased to the vicinity of the maximum or dangerous temperature at203 (Tmax). Heat transfer volume is increased to level 204. The tubeheating temperature difference is made small and thermal stress to thetube is thus decreased and tube life is longer as well. Tube life in aconventional boiler is reduced due to large temperature changes andresulting thermal stress.

See increase 205 of the heat transfer volume, over a conventional boilerat 206. At the same time, in the invention, when the high temperaturecombustion gas is exhausted through regenerator beds, the sensible heatis recovered to the regenerator, and then heat is returned to thecombustion chamber after it is used for preheating the combustion airagain at high thermal efficiency. this also enables the temperature ofthe combustion air to be high and close to the temperature of combustionexhaust gas which flows into the regenerator, and high thermalefficiency is maintained.

In addition, when each pair of burners is alternatively burned for ashort time, the flame position is changed so often that the flamebecomes non-constant and a greater flatness of the temperature profileis achieved.

As described above, the average temperature at 202, can be increased tothe vicinity of the maximum temperature at 203 and this is possiblebecause of the flatness of the temperature in the combustion chamberwhich is achieved by forced circulation of the combustion gas.Therefore, since the heat transfer volume can be increased at 205, thesame evaporating volume as in conventional boiler's which has aconvection heat transfer section, can be secured, even only by using theradiation heat transfer section. At the same time, since thermalrecovery is made by the regenerator bed, high thermal efficiency ismaintained.

What is claimed is:
 1. A method of operating a boiler with increasedflame temperature and output, the boiler having a combustion chamber; aradiation heat transfer section in the combustion chamber; and at leastone regenerative-heating burner system connected to the combustionchamber, the regenerative-heating burner system having a pair ofregenerative beds and a burner connected to each bed; the methodcomprising:supplying heat combustion air through each regenerative bedand to each burner at a jet flow rate of at east 60 m/s; supplying thecombustion air with fuel to each burner system for forming a flame whichproduces combustion gas which is exhausted into the combustion chamberand past the radiation heat transfer section, the flame being at a firsttemperature and the combustion gas being at a second temperature, thecombustion air having a temperature preheated to above the ignitiontemperature of the fuel; causing a flow of said combustion air and flowof said combustion gas to be changed over, relative to each other, forfirst heating one of the regenerative beds with combustion gas passingtherethrough to a temperature above the ignition temperature of thefuel, while combustion air is being supplied through the other one ofthe regenerative beds for being heated to above the ignition temperatureof the fuel before combining with the fuel to form the flame; andheating the combustion air in the regenerative beds to above theignition temperature of the fuel and substantially to the sametemperature as said second temperature of the combustion gas, so thatthe first temperature of the flame is increased to increase heattransfer to the radiation heat transfer section while creating asubstantially flat and high temperature across the combustion chamber.2. A method according to claim 1, including providing in said boiler aheat exchanger which only includes said radiation heat transfer section,and extending heat recovery means through said radiation heat transfersection for absorbing heat from the boiler.
 3. A method according toclaim 1, including a plurality of regenerative-heating burner systems insaid combustion chamber, a convection heat transfer section connected tosaid radiation heat transfer section for receiving at least a portion ofsaid combustion gas which is exhausted from the boiler, a remainder ofthe combustion gas which is not exhausted from the boiler beingrecirculated to at least some of the regenerative beds of said pluralityof regenerative-heating burner systems.
 4. A method according to claim3, including extending heat recovery means through at least one of saidradiation heat transfer section and said convection heat transfersection, for absorbing heat from the boiler.
 5. A method according toclaim 1, including producing said combustion gas to have said secondtemperature to be about 700° to 1,000° C., by supplying said combustionair and fuel so that said first temperature of said flame is betweenabout 1,800° to 2,000° C.
 6. A method according to claim 1, including asuperheater section connected to said radiation heat transfer sectionfor receiving some of the combustion gas, passing fluid through saidsuper-heater section for forming saturated steam, said super-heatersection constructed for passing all of the exhaust gas supplied theretofrom the radiation heat transfer section, out of said boiler.
 7. Amethod according to claim 6, including controlling the amount ofcombustion gas passing from the radiation heat transfer section of thesuper-heater section, as a function of a temperature of the super-heatedsteam.
 8. A method according to claim 1, including changing over atintervals of about 20 seconds to about 2 minutes for varying theposition of the flame in the combustion chamber for increasing aflatness of the temperature level across the combustion chamber.
 9. Amethod according to claim 8, wherein the interval is about 20 seconds to40 seconds.
 10. A method according to claim 9, including supplying thecombustion air at a flow rate of above 100 m/s.
 11. A method accordingto claim 8, including supplying the combustion air at a jet flow rate ofabove 80 m/s.